Applicator system for hot melt adhesive and the like



I Oct. 24, 19,67 LOCKWOOD 3,348,520

APPLIQATOR SYSTEM FOR HOT MELT ADHESIVE AND THE LIKE Filed Sept. 16,1965 2 Sheets-Sheet 1 20 29 22 J7 I fllfifi 27 25 34 12 g 59 $3 2 j; QHull 42 $19 J4 24 16" v 3; a0 32 40 g 15 2 Y L a x 7 4 d F ///f 28 in nm40 .flvme'urbe fz 32a Giana/ALE lame 400019,

- @EGAQLSQM E Q Oct. 24, 1967 G. H. LOCKWOOD 3,348,520

APPLICATOR SYSTEM FOR HOT MELT ADHESIVE AND THE LIKE Filed sept. 16,1965 2 Sheets-Sheet 2 as I 1 Va/ye 7 fZ (em trier I I JNVEA/ra/e 134- vI GLy/WV {LOG/(W002?) BMQQM United States Patent 3,348,520 APPLICATORSYTEM FOR HOT MELT ADHESIVE AND THE LIKE Glynn H. Lockwood, CarmelValley, Califi, assignor to Lockwood Technical, Inc., Sand City, Calif.,a corporation of California Filed Sept. 16, 1965, Ser. No. 487,699

8 Claims. (Cl. 118-2) ABSTRACT OF THE DISCLOSURE Particularly eifectivepressure-actuated valve structures are incorporated in nozzles forapplying hot melt adhesive and the like to a moving work surface. Thevalves are operated simultaneously by pressure pulses developed in theadhesive by a piston pump intermittently driven under fluid control andreceiving adhesive from a melt tank through a check valve. Improvedoperation is obtained by omission of any pump outlet valve, and bylimiting the inlet flow to the pump to produce a controlled negativepressure during the suction stroke.

This invention has to do generally with systems for applying to a Worksurface a liquid material in a definite and controllable'applicationpattern.

Certain aspects of the invention are especially useful in connectionwith systems for applying hot melt adhesive to such work surfaces as theflaps of paperboard cartons or cases to effect sealing. The inventionwill be de- 1" e t "1 SC 1b d Wlth speclal reference to such systems butW1 h be carried out. Theparticulars of that description, and of outimplying limitation to any particular type of liquid or work surface.

For sealing such objects as cartons, hot melt adhesive is preferablyapplied in a definitely predetermined pattern that will insure propersealing and at the same time avoid wasting adhesive. In some instancesit is also desirable to obtain a seal of accurately limited strength tofacilitate opening. The present invention permits particularly flexible,accurate and reliable control of the application pattern, which mayinclude not only accurately placed dashes or stripes on the moving worksurface but also short dots applied at'high cycling rate. V

The present invention utilizes an intermittently driven pump forpressurizing thefluid supplied to the applicator nozzles during thoseperiods when fluid is to be applied to thework surface, and fluidapplication is terminated by terminating the pressure pulse produced bythe pump.

One aspect of the invention provides a check valve closely adjacent eachnozzle orifice. When several nozzles are supplied with fluid in parallelfrom a common pump and via a common conduit or header chamber, the checkvalve for each nozzle is preferably inserted between that nozzle and theconduit or header chamber. In a preferred arrangement, a header chamberis supplied with fluid from' the pump via a single conduit, which may bebranched for supply to other header chambers, and a plurality of nozzleorifices communicate via respective check valves with .each headerchamber. If the pump is located close to the header chamber no conduitis required. The pump is typically of reciprocating type, with thepressure cylinder preferably connected directly, that is, without anyintervening valve structures, with the header chamber or cham-v bers.

A further aspect of the invention involves pump structure that producesthe desired'supply pressure on the pressure stroke and produces adistinctly negative pressure in the header chamber or chambers on thesuction stroke. Such subatmospheric pressure is obtainable by thecombination of suitably restricted supply of fluid to the pump incombination with the described open communication 3,348,526) PatentedGet. 24, 1&6?

between the output side of the pump and the header cham her. With thatarrangement relatively long conduits can be successfully used.Transmission of the negative pressure the entire length of the conduitdirectly tothe check valve at each nozzle insures prompt and cleanclosure of the check valves, cutting 01f the fluid delivery sharply andpreventing any tendency toward dripping from the nozzles.

A further aspect of the invention provides improved check valvestructures which are remarkably prompt and reliable in operation, bothin opening in response to an applied pulse of fluid pressure and inclosing in response to sharply reduced or negative pressure. Suchimproved operation is attained by providing a control orifice of limitedsectional area through which fluid flows when the valve is open, andapplying the pressure drop developed by that orifice to a pistonstructure that is coupled to the valve. Whereas such structure utilizesan appreciable portion of the available fluid supply pressure inoperation of the valve, the resulting speed and uniformity of the valveoperation is highly desirable. That is particularly true 7 h whenseveral nozzles are to be supplied through respective check valves froma common pressure source.

In addition to the improved operating characteristics described above,the systems of the present invention are unusually simple and economicalto construct and install,

and are remarkably versatile in operation that are obtainable.

A full understanding of the invention, and of its further objects andadvantages, will be had from the following description of certainillustrative ways in which it may the detailed design and theaccompanying drawings which form a part of it, are intended only asillustration, and not as a limitation upon the scope of the invention,which is defined in the appended claims.

In the drawings:

FIG. 1 is an-elevation, partly in axial section, representing a portionof an illustrative nozzle block with valved nozzles in accordance withthe invention;

FIG. 2 is an axial section corresponding to a portion of FIG. 1 andshowing a nozzle valve in open position;

FIG. 3 is an axial section corresponding generally to FIG. 2 and showinga modification;

FIG. 4 is an axial section showing a further modification; and 7 FIG. 5is a vertical section showing an illustrative intermittentpressurizingsystem in accordance with the invention.

Referring first to FIGS. 1 and 2, an elongated nozzle block isrepresented fragmentarily at 10, with header chamber 12 through whichthe fluid to be applied is distributed to the nozzles 14 for applicationto a work sur-' face 19. Fluid is supplied to chamber 12 via the tube16, which is typically at least somewhat flexible. If the liquid to beapplied is a hot melt adhesive, for example, the entire block assemblyis preferably maintained at elevated temperature, as by individualelectric heating units indicated at 17 and controlled by one or morethermostatic switches 18. Conduit 16 is then preferably surrounded by athermostated heating jacket, which may be of conventional type and isindicated only schematically at 15. The other end of conduit 16 isconnected to a suitable intermittent source of pressurized fluid, suchas that to be illustratively described. A wide variety of nozzleconfigurations may be employed. For example, block 10 may be of anyrequired length, wit-h a row of applicator nozzles 14 distributed asdesired along the length of chamber 12. Or block 10 may extendappreciably in a direction perpendicular to the plane of FIG. 1, withnozzles 14 arranged as desired in a two-dimensional array.

Also, several blocks may be connected, as via branch conduits, to asingle fluid supply conduit such as 16. Alternatively, a suitable pumpmechanism for producing intermittently pressurized fluid may feeddirectly into chamber 12, without any distinct conduit structure.

Each nozzle shown illustratively in FIGS. 1 and 2 comprises a body 20 ofgenerally cylindrical form with external threads at its rearward end formounting it in sealed relation in a threaded bore in block 10. Body 20has an axial through bore that is counterbored and threaded at itsforward end at 21. An internal flange 25 forms a forwardly facing,generally conical valve seat 22 and divides the bore into a forward ornozzle chamber 23 and a rear or entrance chamber 24. The nozzle propercomprises a coaxially bored tip 26 mounted in chamber 23 for axialadjustment by means of the threads 21 and provided with sealing meansshown as the O-ring 27. The axial nozzle orifice 28 in tip 26 produces awell defined jet of liquid that typically carries for an appreciabledistance to the work surface, indicated at 19. The direction of that jetdelivery may have any desired orientation with respect to gravity.

The valve element 30 comprises the valve head 32 with conical orspherical working face, and the valve stem 34 which extends upstreamfrom the head and is threaded to carry the cylindrical piston member 36.A suitable spring is provided to yieldingly urge the valve elementrearwardly to seat the valve. Such a spring is shown illustratively at40 in chamber 24 acting between the rear face of flange 25 and ashoulder 37 on the piston member. Alternatively, the spring 40 may be ofsomewhat larger diameter positioned in header chamber 12 and actingbetween the extreme rearward face of body 20 and an external flange atthe rear end of piston member 36. In either case, the force tending toclose the valve is variable by adjustment of the piston member onthreaded stem 34. That adjustment of the piston member is locked bymeans of the set screw 39, typically provided'with an Allen head. Thepiston member includes a cylindrical body portion 38 to the rear ofshoulder 37 which has a diameter nearly equal to that of entrancechamber 24, leaving an annular passage or control orifice 42 of smallradial dimension. In closed position of the valve, piston body 38protrudes rearwardly from the main housing bore, so that only itsforward portion directly opposes the chamber wall. As the valve elementmoves forward to open the valve (FIG. 2), control orifice 42 islengthened, increasing the resistance to fluid flow. The length of thecontrol orifice, and hence its flow resistance, also varies with theaxial position of piston member 36 on the valve stem. Forward movementof valve element 30 is limited by the rearward face of nozzle tip 26.Either that face or the opposing face of the valve element is channeledor otherwise formed as at 33 to provide ample fluid flow into the tipbore 28 despite that contact. I

In operation of the described valve structure, the valve is normally inclosed position of FIG. 1, with the fluid pressure in header chamber 12below a positive threshold value determined by the adjustment of spring40. To apply adhesive, the pressure supplied to the header is abrutlyraised above that threshold. The force thereby developed on the valveelement, acting as a piston, compresses spring 40 and opens the valve.The effective piston area for initial opening of the valve isessentially the area inside valve seat flange 25. Once the valve hasopened, pressure on both sides of the valve head (FIG. 2) tends to beequalized by the relatively free flow through the valve (FIG. 2). With aconventional valve, that often leads to an equilibrium condition inwhich the valve-opening pressure is barely suificient, or eveninsufiicient, to hold the valve open, causing chatter or othermalfunction of the valve.

In the present structure, on the other hand, once the valve is open ittends to remain stably in that condition. Flow through the resistancedue to the small section area of control orifice 42 produces anappreciable pressure drop that increases with fiow through the valve.The fluid pressure in entrance chamber 24 is therefore appreciably lessthan the supply pressure in header chamber 12. That pressure differenceacts on piston member 3&5, the effective area of which is typicallylarge compared to the actual valve orifice, producing a forward forcethat tends to hold the valve open. Moreover, the viscous drag of thefluid flowing in control orifice 42 in contact with piston body 38produces a further force tending to open the valve. Neither of thosevalve-opening forces is present to a significant extent in aconventional check valve in open position. Their effect in the presentvalve is to stabilize the valve in open position by a kind of positivefeedback action.

Upon termination of the pressure pulse supplied to header chamber 12,the valves are all promptly closed by action of their return springs 40.If the header chamber is reduced at cutoff to a pressure less thanatmospheric, as is preferred, a reverse pressure drop is establishedacross control orifice 42, rendering the valve closing action moreprompt and reliable. The valve structure thus tends to increasestability of operation both for opening and closing of the valve.

That stabilizing action greatly facilitates satisfactory operation of aplurality of valved nozzles supplied from the same header block, and isespecially valuable for operating several such nozzles from the samesupply line 16. When a pulse of fluid pressure is supplied to chamber 12there is initially no flow out of the chamber, and the header pressuretends to rise to the full supply pressure. If that pressure exceeds thevalve-0pening threshold, all valves may be opened, at least momentarily.The resulting flow, however, reduces the header pressure appreciably,due to pressure drop in conduit 16. With check valves of conventionaltype, that reduction may well go below the threshold pressure,permitting some of the valves to close. The practical effect is usuallyerratic and unreliable valve operation, and correspondingly irregulardelivery of fluid to the work surface. With the present valvestructures, even if the pressure in header chamber 12 drops under steadyflow conditions below the threshold needed initially to open the valves,that pressure is still ample to prevent valve closure due to the pistonand viscous actions that have been described. It is there fore feasibleto operate a plurality of nozzles from the same supply line even with asupply pressure that exceeds the valve-opening threshold by only amoderate excess.

' That threshold is readily adjustable by shifting piston member 36 onthe valve stem to vary the tension of spring 41 Moreover, suchadjustment automatically varies the length of control orifice 42correspondingly, making that passage longer as the spring tension isincreased. Hence the stabilizing pressure drop that'tends to hol-d'thevalve open increases automatically with the spring tension tending toclose the valve. That combination of two coordinated results in a singleadjustment operation is ordinarily highly convenient. If preferred, ofcourse, separate adjustments can be provided for the two functions, asby forming spring shoulder 37 on a sleeve threaded on valve stem 34 andmaking piston body 38 threadedly adjustable 011 external threads on thatsleeve.

Ordinarily the rate of delivery of fluid from nozzle 14 is mostconveniently adjustable by variation of the fluid supply pressure at theintermittent source, as will be described. However, further adjustmentof the delivery rate is available by axial adjustment of tip 26. As thattip is screwed forward, valve element 30 is permitted to mover fartherforward in open position. With suitable dimensioning of the parts, thenozzle tip may be screwed home to lock the valve closed, providingconvenient selection of the active nozzles for a desired pattern.

FIG. 3 represents in axial section a modification of the structure ofFIGS. 1 and 2, whereby the control orifice 42a is located downstream ofthe valve itself and is variable together with the spring force byadjustment of the nozzle tip 26a. The latter is threaded into theforward end of the main body bore, as in the previous form, but carriesa rearwardly extending integral sleeve formation 50. The valve head 32acarries an integral forwardly extending sleeve formation 52 which istelescopically received within tip sleeve 50 with a small radialclearance. The two sleeves thus define a generally annular passage 42aof limited radial dimension. That passage corresponds generally infunction to control orifice 42 of the previous embodiment. A spring 40ais received within sleeve 52 and acts between the valve element and thenozzle tip. Axial adjustment of that tip thus varies the spring tensionand also varies the length of control orifice 56. As illustrated, thatorifice is relatively short in closed position of the valve andincreases in length with opening movement of the valve element. Thatmovement is positively limited by the nut 54, which is threaded on thevalve stem 34a and engages a rearwardly facing shoulder 55 on the valvebody. Channels 57 are formed in the forward portion of the nut insuringessentially free fluid flow in fully open position of the valve. Themodification of FIG. 3 thus provides adjustments that functionallycorrespond to those of the previous embodiment, but the functions of thetip adjustment and the valve stem nut adjustment are interchanged.

FIG. 3 further illustrates that the flow resistance in the controlorifice can be made to vary with the position of the valve element bymaking the opposing walls of the orifice slightly conical, so thatrelative axial movement of the walls directly alters the radial spacingbetween them. In FIG. 3 such variation of radial dimension of controlorifice 42a is combined with simultaneous variation of the effectivelength of the orifice. The same effect may be obtained in themodification of FIGS. 1 and 2 by making the opposing walls of controlorifice 42 slightly conical. A variety of similar effects are obtainableby using different conical angles on the two walls, or by making onewall conical and the other right cylindrical. The term conical in thisconnection is intended to include functionally similar forms, which mayinclude curves or. step functions of varying radius rather than strictlyconical surfaces.

The invention is further illustrated by the structure shown somewhatschematically in FIG. 4. The housing 60 encloses a cylindrical chamber62 in which the valve element 70 is axially slidable. The annular valveseat 65 is formed on the end of tube 66, coaxially threaded into theinner end wall 67 of housing 60. That tube may connect the valve to asuitable source of intermittently pressurized fluid, either directly orvia a header chamber or a preferably flexible conduit. Valve element 70comprises a cylindrical body portion 72 and a valve portion 74. Bodyportion 72 preferably fits closely but freely in the valve chamber andis provided with a suitable seal, shown as the O-ring 73. At its innerend the valve element carries a valve formation 76, adapted to sealinglyengage valve seat 65 in response to inward movement of the valveelement. That engagement acts as a limit stop for such movement, whichis yieldingly urged by the com pression spring 80, acting between theshoulder 77 on the valve element and an internal collar 82, adjustablythreaded in the end of housing 60. Collar 82 also functions as apositive stop, being engaged by the shoulder 79 on the valve element tolimit outward movement of the later. Threaded adjustment of collar 82permits coordinated variation of the degree of valve opening and thespring tension.

Fluid from chamber 62 enters the axial bore 87 in the valve element viathe radial passages 88, and is then delieverd through the axial nozzleorifice 86 of relatively small diameter. Orifice 86 not only acts asdelivery nozzle, but during outward fluid flow develops a pressure dropthat is effectively applied to the entire inner axial face of the valveelement, tending to hold the valve open so long as an appreciable supplypressure is maintained in tube 66.

When the operating pressure pulse is terminated, the valve is returnedto closed position by spring 80. If, as is preferred, the cutoffpressure in tube 66 is less than atmospheric, fluid tends to be drawninward through nozzle orifice 86, and the pressure drop developed bythat flow aids the closing movement of the valve. The present structureis similar to the previous forms in utilizing piston action to stabilizethe valve operation, but differs in that the forward face of the pistonstructure is exposed to atmospheric pressure rather than to a fluidpressure upstream of the nozzle orifice. However, nozzle orifice 86 inthe present structure may be considered to establish the pressuredifferential between substantially the whole supply pressure acting onthe inner piston face within chamber 62 and atmospheric pressure actingon the outer piston face outside that chamber. As in the previousembodiments, the effective piston area is larger than the area of thevalve orifice, the latter being approximately equal to the insidediameter of tube 66.

Pressurized fluid may be supplied intermittently to nozzle structures ofthe described type in many different ways. For example, a continuouslyoperating pump may supply pressure to a switching valve that is operatedby solenoid control or the like to connect the nozzles via a suitableconduit alternatively to the output and to the input sides of the fluidpump, thereby supplying either a relatively large supply pressure or asubatomspheric cutoff pressure to the nozzle structures.

FIG. 5 represents a preferred supply system in which a fluid pump ofreciprocating type is actuated intermittently only when fluidapplication to the work surface is required. Following each suchactuation, the pump is returned to rest position and is therebyrecharged and ready for another actuation. In ordinary practice, thepump stroke capacity is abundantly adequate to maintain application forthe longest continuous application periods that are required.

In FIG. 5 an open melt tank is represented at 90, with insulatinghousing 92 and removable cover 93, mounted in heat insulated relation ona supporting frame 94. Heaters are mounted in suitable bores 96 in thebody of the tank, and are thermostatically controlled in known manner bya temperature probe in the bore 97. The tank accepts hot meltcompositions in slab, pellet or chunk form, melting the material andraising it to the desired temperature for delivery through the filterscreen 103 to the outlet opening 104 in the tank bottom. The pump blockis mounted in close heat conducting relation to the bottom of tank 90,with the inlet passage 102 to the pump communicating with tank outlet104. An O-ring seal 105 is provided between the tank and the pump block.The passage 102, 104 is provided with a check valve, shown as the hollowball 106 which normally floats in the fluid melt, engaging thedownwardly facing valve seat 107 and preventing upward flow.Alternatively, a conventional solid ball may be used, spring-urgedupward by a coil spring. Downward movement of ball 106 to open the valveis limited by the stop rod 108, which is threaded in sealed relation inthe valve block and is accessible for adjustment from below. The lightball makes a valve spring unnecessary, and the valve then opens inabsence of fluid, making the pump self priming. The low mass of the balloffers the further advantage of fast response to changes in direction offluid flow.

The pump cylinder comprises a horizontal bore 110 in pump block 100,communicating at its inner end with pump inlet 102. Pump outlet 112 istypically coaxial with cylinder 110, though additional outlets maydiverge in other directions in any desired number. Outlet 112communicates directly and without any intervening valve structure withheader chamber 12 of FIGS. 1 to 3, for example, either directly or viasupply conduit 16, typically heated in known manner. The pump piston 114slides in cylinder 110 with suitable seals 115. The piston is driven bythe rod 116, preferably connected through a universal joint indicated at117. Rod 116 may be driven by any desired type of two-way actuator thatresponds with suitable speed and power to a .control signal. Actuatorsof electrical, hydraulic and pneumatic types are well known. The presentillustrative actuator will be described as pneumatic, but with simplemodifications may be considered as hydraulic instead.

A double-acting air cylinder is represented at 1219 with piston 122 andinlet conduits 124 and 126 at its inner and outer ends, respectively.Compressed air from a source such as a continuously operated compressor128 is supplied to conduits 124 and 126 via the solenoid operatedfour-way valve indicated schematically at 130. That valve normallysupplies air to conduit 124 and opens conduit 126 to the atmosphere,driving pump piston 114 outward in its cylinder, that is, to the rightas seen in FIG. 5. A charge of fiuid is thereby drawn into pump cylinder110 from tank 90 via check valve 105. Energization of air valve 130, asby an electric pulse delivered over the line 132 from a suitable switchdevice 134, shifts the compressed air to conduit 126 and opens conduit124 to the atmosphere, driving pump piston 114 inward and pressurizingthe fluid melt in cylinder 110 and throughout supply conduit 16. Fluidflow back to tank 90 is prevented by check valve 106. When the system isemployed for the illustrative purpose of sealing cartons, switch 134, istypically controlled in known manner by one or more mechanical feelerarms that engage the cartons as they pass the applicator nozzles. Thefluid pressure during delivery pulses, and hence the rate of fluiddelivery at each nozzle, is conveniently adjustable by variation of theair pressure supplied at 128. Actuator120 is preferably also providedwith adjustable limit stops, not explicitly shown, by which the lengthof the piston stroke during each actuation can be limited if desired.Further convenient control of the actuator operation is obtainable byutilizing at 130 a fourway control valve that has separate exhaust portsto atmosphere for exhaust from line 124 and from line 126, and providinga variable flow-limiting orifice in the exhaust from line 124. Thatorifice then controllably limits the rate of the fluid delivery strokeof pump 120 without affecting other aspects of the cycle.

Itwill be noted that in the present preferred system supply conduit 16communicates directly and without any intervening valve structurewhatever with the working face of pump piston 114. Hence the full pumppressure during the compressing stroke is delivered to that conduit;and, during the return stroke of the piston, conduit 16 is exposed towhatever sub-atmospheric pressure is produced in pump cylinder 110. Themagnitude of that negative pressure is readily adjustable by varying thesetting of stop pin 108 to control the extent to which check valve 106is permitted to open. As that opening is decreased, for example, therate of fluid supply to the pump during its return stroke iscorrespondingly dereased, producing a more negative pressure in conduit16. The rate of piston return is correspondingly reduced, but it isfound in practice that for most application patterns that are requiredthe intervals between pattern elements :allow ample piston return timeeven with considerable throttling at valve 106.

In general, the greater the magnitude of the negative pressure developedduring the pump return stroke and transmitted to the nozzle headerchamber or chambers, the more sharp and reliable is the closure of thecheck valves at the respective nozzles. When a plurality of nozzles withtheir respective check valves are operated from a single supply conduit,the described valve structure with piston assisted actuation greatlyaids the uniformity and stability of operation of all nozzle valves.

I claim:

1. A system for applying to .a work surface that is movable along a patha viscous hot melt adhesive in a controlled pattern of parallel linesegments, said system comprising in combination structure forming a hotmelt t-ank open to atmospheric pressure and adapted to receive solidadhesive,

means for controllably heating the tank structure to melt adhesive inthe tank,

structure forming a pump cylinder thermally integrated with said tankstructure, said cylinder containing an axially reciprocable pump pistonand communicating with the tank interior via a check valve for admittingliquid adhesive to the cylinder during suction movement of the piston,

a piston actuator mechanically coupled to the piston to drive the pistonin intermittent cycles of movement in response to control fluid pressurepulses supplied to the actuator, each piston cycle comprising a deliverystroke followed by .a suction stroke,

structure forming a header chamber having a chamber wall with aplurality of mutually spaced through bores therein, said headerstructure being adapted to be mounted with said wall in spacedly opposedrelation to said work surface path and with the bore spacing transverseof said path,

a conduit connecting the header chamber to the pump cylinder, saidconduit being continuously open for flow of liquid adhesive therebetweenin both directions,

a plurality of nozzle structures mounted in the respective through boresin said header chamber wall and forming respective nozzle orifices thatcommunicate in parallel with the header chamber,

an individual normally closed valve for each nozzle orifice normallyclosing the communication between that orifice and the header chamberand actuable, in response to presence in the header chamber of fluidpressure exceeding a predetermined threshold value, to permit outwardflow of adhesive from the header chamber to the orifice to apply a linesegment of adhesive to the work surface,

and means for supplying to said actuator control fluid pressure plusesin timed relation to the work surface movement and of suificientmagnitude to make the adhesive pressure in the header chamber at leastmomentarily exceed said threshold value and thereby to open all thenozzle valves effectively simultaneously.

2, The combination defined in claim 1, and in which each said nozzlestructure and valve comprise a generally cylindrical body having apassage with a forwardly facing shoulder forming a valve seat, structureforming said nozzle orifice at the forward end of the passage andclosely adjacent the valve seat,

a valve element axially movable in the passage and having a closureportion adapted to sealingly engage the valve seat' by virtue ofrearward movement of the valve element,

means yielding urging the valve element rearwardly to' close the valve,

the valve element having a generally cylindrical portion that forms withthe passage wall a generally annular and axially elongated controlorifice of limited sectional area through which fluid flows in serieswith the valve when the valve is open,

the sectional area of the control orifice throughout its axial lengthbeing so limited with relation to the nozzle orifice that such flowexerts an appreciable viscous drag on the valve element tending to holdthe valve open.

3. The combination defined in claim '2, and in which said generallycylindrical portion of the valve element is axially adjustablerelatively to the closure portion of the valve element to vary theeffective length of the control orifice.

4. The combination defined in claim 2, and in which said means yieldingurging valve closure include means adjustably movable to vary theyielding force exerted on the valve element,

movement of the last said means acting to vary the axial length of saidcontrol orifice in the same sense as said force variation.

5. The combination defined in claim 1, and in which each said nozzlestructure and valve comprise a generally cylindrical body having anaxial through passage with a forwardly facing shoulder forming 10 andmeans for adjustably limiting the rate of flow from the tank interior tothe pump cylinder to produce an adjustalbly variable subatmosphericpressure in the cylinder during the suction stroke of the pump pistonand thereby insure closure of said valves.

8. The combination defined in claim 7, and in which the last said meanscomprise structure adjustably limiting the degree of opening of saidcheck valve.

a valve seat,

a valve element axially movable in the passage in sealed relationtherewith and having a portion adapted to sealingly engage the valveseat by virtue of rearward movement of the valve element,

structure forming said nozzle orifice at the forward end of said valveelement in open communication with the passage between the valve seatand the valve element seal,

and means yielding urging the valve element rearwardly in the passage toclose the valve. References Cited 6. The combination defined in claim 1,and including UNITED STATES PATENTS means for adjustably limiting therate of flow through 2 898 820 8/1959, Keely 118 2 X said communicationbetween the tank and the pump 3130'876 4/1964 Baker "118410 X cylinderwhen the check valve is open, to produ e 3146126 8/1964 Baker 118 2 anadjustably variable subatmospheric pressure in 3246625 4/1966 Beamal;118 2 the header chamber during the suction s roke of 5286:6559 11/1966Ziemba the Pump Plston- 3,292,191 12/1966 Kamborian 118410 X 7. A systemfor applying to a work surface that 1s 3 315 899 4/1967 Quarve 239 119 Xmovable along a path a viscous hot melt adhesive in a 1555797 9/1925Gramme; controlled pattern of parallel line segments, said system2077938 4/1937 Kuttner 19 X comPnsmg cimbmatlon 2,680,652 1/1954Kooistna 239 119 X structure forming a hot melt t-ank open to atmos-2686 562 8/1954 Maccracken et a1 pheric pressure and adapted to receivesolid ad- 2747555 5/1956 Bummer X hesive, means for controllably heatingthe tank structure t 2323f. 3 2 melt adheslve the tank 3,118,611 1/1964Berlyn 239-119 X structure forming a pump cylinder containing an axral-3 174 6,89 3/1965 McIntyre 239 583 X ly reciprooable pump piston andcommunicating n with the tank interior via a check valve for admit-FOREIGN PATENTS ting liquid adhesive to the cylinder during suction 701780 12/1953 Great Britain movement of the piston,

a piston actuator for driving the piston in intermittent cycles ofmovement in timed relation to the work surface movement, each pistoncycle compris- M. HENSON WOOD, ]R., Primary Examiner.

V. C. WILKS, Assistant Examiner.

7. A SYSTEM FOR APPLYING TO A WORK SURFACE THAT IS MOVABLE ALONG A PATHA VISCOUS HOT MELT ADHESIVE IN A CONTROLLED PATTERN OF PARALLEL LINESEGMENTS, SAID SYSTEM COMPRISING IN COMBINATION STRUCTURE FORMING A HOTMELT TANK OPEN TO ATMOSPHERIC PRESSURE AND ADAPTED TO RECEIVE SOLIDADHESIVE, MEANS FOR CONTROLLABLY HEATING THE TANK STRUCTURE TO MELTADHESIVE IN THE TANK, STRUCTURE FORMING A PUMP CYLINDER CONTAINING ANAXIALLY RECIPROCABLE PUMP PISTON AND COMMUNICATING WITH THE TANKINTERIOR VIA A CHECK VALVE FOR ADMITING LIQUID ADHESIVE TO THE CYLINDERDURING SUCTION MOVEMENT OF THE PISTON, A PISTON ACTUATOR FOR DRIVING THEPISTON IN INTERMITTENT CYCLES OF MOVEMENT IN TIMED RELATION TO THE WORKSURFACE MOVEMENT, EACH PISTON CYCLE COMPRISING A DELIVERY STROKEFOLLOWED BY A SUCTION STROKE, STRUCTURE FORMING A PLURALITY OFDISPENSING NOZZLES MOUNTABLE ADJACENT THE WORK SURFACE PATH ANDCOMMUNICATING IN PARALLEL WITH THE PUMP CYLINDER, AN INDIVIDUAL NORMALLYCLOSED VALVE FOR EACH NOZZLE NORMALLY CLOSING THE COMMUNICATION BETWEENTHAT NOZZLE AND THE CYLINDER AND ACTUABLE IN RESPONSE TO ADHESIVEPRESSURE TO PERMIT OUTWARD FLOW OF ADHESIVE FROM THE NOZZLE, AND MEANSFOR ADJUSTABLY LIMITING THE RATE OF FLOW FROM THE TANK INTERIOR TO THEPUMP CYLINDER TO PRODUCE AN ADJUSTABLY VARIABLE SUBATMOSPHERIC PRESSUREIN THE CYLINDER DURING THE SUCTION STROKE OF THE PUMP PISTON AND THEREBYINSURE CLOSURE OF SAID VALVES.